Our investigation into the morphogenesis of bacteriophage will be continued, with emphasis on two aspects: (1) the detailed mechanisms of T4 phage tail fiber assembly and attachment, and (2) characterization of the DNA packaging reactions of bacteriophages T4 and T7. 1) The assembly and attachment of T4 tail fibers requires four proteins, under phage genetic control, which are not found in the completed structure. Biochemical and genetic approaches will be followed in attempts to understand the mechanisms by which these proteins promote or direct the assembly of the structural protein components of the tail fibers. 2) Using an in vitro system for T7 DNA packaging similar to those described in the literature, we shall investigate the effects of varying reaction conditions, including ionic environment, presence of inhibitors, temperature, and pressure, on the packaging reaction. In addition we shall determine whether intermediate structures in the packaging reaction can be demonstrated and characterized.